Absorbent gelling materials (also referred to as hydrogels, superabsorbent, or hydrocolloid materials, and hereinafter alternatively referred to as "AGM," or in the plural, "AGMs") are capable of absorbing large quantities of liquids such as water and body exudates and of retaining such absorbed liquids under moderate pressures. These absorption characteristics make them especially suitable for use in disposable absorbent articles such as diapers, sanitary napkins, incontinent devices and the like. Particulate AGMs are typically disposed in and/or on webs of absorbent fibers in the absorbent core component of such articles. For example, U.S. Pat. No. 3,699,103 issued to Harper et al. on Jun. 13, 1972 and U.S. Pat. No. 3,670,731 issued to Harmon on Jun. 20, 1972 both disclose the use of particulate AGM in absorbent articles.
Conventional particulate AGMs, however, have the limitation that the particles are not immobilized and are free to migrate during processing and/or use. Migration of the particles during processing can lead to material handling losses during manufacturing operations and, more significantly, the nonhomogeneous incorporation of the particles into structures in which the particles are being used. Nonhomogeneous incorporation of the particles can result in regions of relatively high concentration of the particulate material. When the particles are wetted, such high concentration regions tend to exhibit high resistance to liquid flow, i.e., gel blocking. Gel blocking is a particular problem where relatively high gel volume, low gel strength AGMs are used. As a result, the acquisition and/or distribution of liquids by the absorbent article is diminished, leading to inefficient utilization of the article and/or leakage.
As a result of product design or migration, the particles may be present in the vicinity of the topsheet or backsheet. The presence of the absorbent particles in these regions tends to cause a gritty feeling to the wearer, pinholing of the backsheet resulting in aesthetic negatives and/or leakage, and/or migration through the topsheet causing gel on the wearer's skin.
One approach to address the migration of particulate hydrogels in absorbent articles is disclosed in U.S. Pat. No. 3,901,236 issued to Assarsson et al. on Aug. 26, 1975. Assarsson discloses particulate hydrogels substantially coated with fibers, for example, conventional wood pulp fibers. Other composites comprising particulate absorbent materials with fibers, such as synthetic polymeric fibers or conventional wood pulp fibers, adhered thereto or embedded therein are disclosed in U.S. No. 5,230,959 issued to Young, Sr., et al. on Jul. 27, 1993 and in U.S. Pat. No. 5,002,814 issued to Knack, et al. on Mar. 26, 1991, respectively.
While some of the problems of reducing migration of particulate AGM materials have been at least partially ameliorated by previously disclosed technology, none has solved the problems in the manner or to the extent of the present invention. For example, it has been found that ordinary wood pulp fibers are less effective than the chemically stiffened, cellulosic fibers in minimizing the migration of AGM particles. In addition, the absorbent efficacy of the aforementioned materials tends to be limited as compared to the absorbent composites of the present invention. In particular, the chemically stiffened, cellulosic fibers tend to impart faster acquisition times, higher rates of fluid absorption, and higher fluid retentions to the composites, as compared to ordinary wood pulp fibers or synthetic polymeric fibers.
Thus, there is an ongoing need to minimize the migration of particulate AGMs in absorbent articles. Moreover, there is a continuing need to improve the absorbent efficacy (including fluid acquisition rates and fluid retentions) of absorbent articles incorporating particulate AGMs. It is especially desirable to provide absorbent articles of the thinnest possible configuration consistent with such absorbent efficacy.
It is therefore an object of the present invention to provide particulate, absorbent gelling materials that are relatively immobile and thus not free to migrate within or out of the absorbent cores of absorbent articles, particularly absorbent cores containing hydrophilic fibers. Another object is to provide absorbent members formed from or containing such particulate, absorbent gelling materials. Still another object of the present invention is to provide absorbent articles containing these absorbent gelling materials, which articles do not suffer from the problems of aesthetics, pin-holing, and/or gel on skin. Yet another object of the present invention is to provide absorbent articles of relatively thin configuration that meet or exceed the absorbent efficacy of absorbent articles known heretofore.